1. Field of the Invention
Embodiments of the invention relate to the processing of substrates. More particularly, embodiments of the invention relate to deposition of tungsten materials on substrates using vapor deposition processes.
2. Description of the Related Art
Semiconductor and electronics processing industries continue to strive for larger production yields while increasing the uniformity of layers deposited on substrates having larger surface areas. These same factors in combination with new materials also provide higher integration of circuits per area of the substrate. As circuit integration increases, the need for greater uniformity and process control regarding layer thickness rises. As a result, various technologies have been developed to deposit layers on substrates in a cost-effective manner, while maintaining control over the characteristics of the layer.
Chemical vapor deposition (CVD) is one of the most common deposition processes employed for depositing layers on a substrate. CVD is a flux-dependent deposition technique that requires precise control of the substrate temperature and the precursors introduced into the processing chamber in order to produce a desired layer of uniform thickness. These requirements become more critical as substrate size increases, creating a need for more complexity in chamber design and gas flow technique to maintain adequate uniformity.
An alternative to CVD process is cyclical deposition or atomic layer deposition (ALD) that demonstrates excellent step coverage. Cyclical deposition or ALD evolved from atomic layer epitaxy (ALE) and employs chemisorption techniques to deliver precursor molecules on a substrate surface in sequential cycles. In simplest form, the cycle exposes the substrate surface to a first precursor, a purge gas, a second precursor, and the purge gas. The first and second precursors react to form a product compound as a film on the substrate surface. The cycle is repeated to form the layer to a desired thickness.
Formation of film layers at a high deposition rate while providing adequate step coverage are conflicting characteristics often necessitating the sacrifice of one to obtain the other. This conflict is true particularly when refractory metal layers are deposited over gaps or vias during the formation of contacts interconnecting adjacent metallic layers separated by dielectric layers. Historically, CVD techniques have been employed to deposit conductive materials such as refractory metals in order to inexpensively and quickly form contacts. Due to the increasing integration of semiconductor circuitry, tungsten has been used based upon superior step coverage. As a result, deposition of tungsten by CVD has wide application in electronic device and semiconductor processing due to the high throughput of the process.
Depositing tungsten by conventional CVD process, however, is attendant with several disadvantages. For example, conventional CVD processes usually cause high aspect ratio (e.g., 20) vias to “pinch-off” and not completely fill during deposition of tungsten films. Also, blanket deposition of a tungsten layer on a semiconductor substrate is time-consuming at temperatures below 400° C. The deposition rate of tungsten may be improved by increasing the deposition temperature to, for example, about 500° C. to about 550° C. However, temperatures in this higher range may compromise the structural and operational integrity of the underlying portions of the integrated circuit being formed. Further, tungsten has proven difficult to uniformly deposit, which typically increases film resistivity.
Therefore, there is a need for an improved process to deposit tungsten-containing materials with good uniformity using vapor deposition techniques.